Field of the Invention
Embodiments of the present invention relate to damping materials having reduced weight than alternative material selections, and more specifically hyperdamping materials and inclusions for application in a variety of structures.
Background
The absorption or attenuation of spectrally broadband vibration and wave energy are goals that have called upon the efforts of researchers spanning diverse engineering and scientific disciplines over the years. While resonant phenomena can facilitate striking vibroacoustic energy trapping, many scenarios involve wide-band or stochastic energy sources for which broadband energy capture is necessary. Typically, the only assured solution for broadband energy attenuation is to introduce excessive mass between the dynamic energy source and the region/receiver of interest, which conflicts with requirements for many applications, such as vehicular systems, where added mass is detrimental to performance and effectiveness. In addition, while input energies may cause vibrations at low frequencies associated with modal oscillations, practical structures transfer the energy to higher frequencies due to joints, friction, and complex geometries, thus creating a ‘noise problem’ in a bandwidth most sensitive to humans through inevitable structure-fluid interaction. Although conventional noise control treatments such as lightweight, poroelastic media are well-suited to dampen waves in this mid-to-high frequency range, they are ill-suited to attenuate low frequency vibrations and sound within typical size constraints. As a result, there is a need for lightweight materials to dampen spectrally broadband vibroacoustic energies.
To address the challenges, strategically architected material systems have been explored that provide elastic and acoustic wave attenuation capabilities not otherwise found in bulk structural materials. Among them, resonant metamaterials and phononic crystals exhibit opportunities to suppress vibration and wave energies due to tuned-mass-damper or bandgap effects. However, despite the advancements, the energy attenuation properties are reliant upon resonance- or bandgap-related phenomena that are often parameter sensitive and narrowband. In addition, many experimental realizations have been proposed using heavy materials including metals and dense rubbers, which are inadequate solutions in the numerous practical applications where treatment weight is a great penalty.
Building upon these ideas, periodic, elastic metamaterials leveraging instability mechanisms are shown to yield remarkable wave propagation control and energy absorption capabilities due to energy changes associated with transitions among internal topologies. On the other hand, these elastic systems are likewise realized by dense materials such as silicones or 3D-printed polymers that are ill-suited for applications where increased treatment density comes at a high cost due to the weight they add to finished products. Static stresses or exterior displacement constraints may also be needed to achieve the wave tailoring properties through the buckling instability, which prevents implementing such metamaterials as absorbers of free field acoustic energy, in the operational mode similar to conventional poroelastic foams. In fact, it is well-known that buckling instability-based phenomena can enhance energy dissipation properties. Such anomalous damping is due to a cancellation of the positive and negative stiffnesses, a design condition termed the elastic stability limit, which eliminates the fundamental natural frequency ωn→0.
Yet, despite the recent advancements the reliance upon parameter-sensitive resonance-related phenomena, the use of dense materials, and possible need for exterior material constraints, make these concepts insufficient solutions for applications demanding lightweight materials for broadband vibration and acoustic energy capture.
With a different material design perspective in mind, other recent studies show that heterogeneous, poroelastic metamaterials can achieve considerable wave and/or vibration energy absorption. For instance, randomly embedding solid, metal inclusions into poroelastic foams improves the low frequency attenuation of the host media. Periodically distributing such inclusions also spawns bandgap phenomena to substantially increase low frequency vibroacoustic energy absorption via “trapped” mode effects. On the other hand, such advancements lack broadband vibroacoustic energy dissipation in a lightweight system design; instead, these poroelastic metamaterials excel at one or another of the individual performance measures.